As a method replacing a conventional radiography, a radiation image recording and reproducing method utilizing a stimulable phosphor is described, for instance, in U.S. Pat. No. 4,239,968 and is practically used. In the method, a radiation image storage panel comprising a stimulable phosphor (i.e., stimulable phosphor sheet) is employed, and the method involves the steps of causing the stimulable phosphor of the panel to absorb radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as "stimulating rays") to release the radiation energy stored in the phosphor as light emission (stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as a visible image from the electric signals After the remaining radiation image is erased from the radiation image storage panel, the panel is prepared for the next radiographic process, that is, the panel is generally used repeatedly after the recorded image is erased.
In the radiation image recording and reproducing method, a radiation image is obtainable with a sufficient amount of information by applying a radiation to an object at a considerably smaller dose, as compared with the conventional radiography using a combination of a radiographic film and a radiographic intensifying screen. Further, the method is very advantageous from the viewpoints of conservation of resources and economic efficiency because the radiation image storage panel can be repeatedly used in the method, while the radiographic film is consumed for each radiographic process in the conventional radiography. The radiation image storage panel employed in the above-described method generally comprises a support and a stimulable phosphor layer provided on one surface of the support. However, if the phosphor layer is self-supporting, the support may be omitted.
As the stimulable phosphor layer, there are known not only a phosphor layer comprising a binder and a stimulable phosphor dispersed therein but also a phosphor layer composed of only an agglomerate of a stimulable phosphor, not containing a binder, which is formed through deposition process or sintering process. The present applicant has already applied for patent with respect to a radiation image storage panel having other type of a phosphor layer in which voids of a stimulable phosphor agglomerate are impregnated with a polymer material (U.S. patent application Ser. No. 184,010 now application Ser. No. 07/462,338). In any of the above-described phosphor layers, the stimulable phosphor emits light (stimulated emission) when excited with an electromagnetic wave (stimulating rays) such as visible light or infrared rays after having been exposed to a radiation such as X-rays. Accordingly, the radiation having passed through an object or radiated from an object is absorbed by the phosphor layer of the panel in proportion to the applied radiation dose, and a radiation image of the object is produced in the panel in the form of a radiation energy-stored image. The radiation energy-stored image can be released as stimulated emission by sequentially irradiating the panel with stimulating rays. The stimulated emission is then photo-electrically detected to give electric signals, so as to reproduce a visible image from the electric signals.
In the case the phosphor layer is provided on a support, a film (i.e., protective film) is generally provided on the free surface (surface not facing the support) of the phosphor layer to protect the phosphor layer from chemical deterioration or physical shock.
The protective film can be formed on the phosphor layer by coating the surface of the phosphor layer with a solution prepared by dissolving an organic polymer material such as a cellulose derivative or polymethyl methacrylate in an appropriate solvent. Alternatively, the protective film can be provided on the phosphor layer by beforehand preparing an organic polymer film such as a film of polyethylene terephthalate; or a sheet for the formation of a protective film such as a transparent glass sheet, followed by placing and fixing it onto the phosphor layer with an appropriate adhesive agent. Otherwise, the protective film can be provided by depositing an inorganic compound on the phosphor layer.
The radiation image storage panel is generally handled or treated under the condition that the panel is shielded from light of outside such as sunlight or room light (namely, under the light-shielded state). The reason is as follows. The stimulable phosphor also absorbs ultraviolet rays and stores energy thereof, so that when the panel is exposed to sunlight or room light (e.g., light of fluorescent lamp), the ultraviolet rays contained in the light is absorbed by the stimulable phosphor and the energy of the ultraviolet rays is stored in the stimulable phosphor. In the reading procedure of a radiation energy-stored image by irradiating the panel with stimulating rays, stimulated emission based on thus stored ultraviolet rays-energy is simultaneously read out to cause occurrence of fogging on the resulting radiation image.
Accordingly, the radiation image storage panel should be handled or treated carefully not to expose the panel to light from outside such as sunlight or room light, and such treatment or handling is sometimes troublesome.
After the radiation image is read from the radiation image storage panel, the panel is irradiated with a light for erasing the remaining radiation image (also referred to hereinafter as "an erasing light"). If the erasing light contains ultraviolet rays, energy of the ultraviolet rays is stored by the stimulable phosphor, while the remaining radiation image is erased by the erasing light, and as a result, the radiation image obtained in the subsequent radiographic process suffers from fogging. Accordingly, it is required to select as the erasing light a light containing less ultraviolet rays, and hence, a light source of the erasing light is restricted.
For coping with the above-described problem, an apparatus for erasing a remaining radiation image of the radiation image storage panel in which the panel is irradiated with an erasing light through an ultraviolet rays-absorbing filter is proposed by Japanese Patent Provisional Publication No. 63(1988)-97939.
However, even if the radiation image storage panel is subjected to the erasing procedure using the above-mentioned specific erasing apparatus, the panel is still required to be treated under the light-shielded state until the next radiographic process.
Further, in the above-mentioned erasing apparatus, even the light useful for the erasing procedure (i.e., erasing light) is also removed (cut off) in a certain amount by the ultraviolet rays-removing filter, so that the erasing efficiency of the apparatus becomes lower than that of the conventional erasing apparatus. Hence, for conducting satisfactory erasure of the remaining radiation image using the above-described apparatus, it is required to use a light source having higher intensity than that used in the known procedures, with the result that a large sized apparatus is required and electric power is considerably consumed.